deviceserver.js

//
// deviceserver.js
//    WebSocket device server
//
// Neil Gershenfeld 
// (c) Massachusetts Institute of Technology 2019
// 
// This work may be reproduced, modified, distributed, performed, and 
// displayed for any purpose, but must acknowledge the mods
// project. Copyright is retained and must be preserved. The work is 
// provided as is; no warranty is provided, and users accept all 
// liability.
//
// check command line
//
if (process.argv.length < 4) {
   console.log("command line: node deviceserver.js client_address server_port")
   process.exit(-1)
   }
//
// start server
//
var client_address = process.argv[2]
var server_port = process.argv[3]
console.log("listening for connection from client address "+client_address+" on server port "+server_port)
var fs = require("fs")
var WebSocketServer = require('ws').Server
wss = new WebSocketServer({port:server_port})
//
// handle connection
//
wss.on('connection',function(ws) {
   //
   // check address
   //
   if (ws._socket.remoteAddress != client_address) {
      console.log("connection rejected from "+ws._socket.remoteAddress)
      ws.send('socket closed')
      ws.close()
      }
   else {
      console.log("connection accepted from "+ws._socket.remoteAddress)
      }
   //
   // handle messages
   //
   var cancel
   ws.on("message",function(msg) {
      //
      // cancel job
      //
      if (msg == 'cancel') {
         cancel = true
         }
      //
      // start job
      //
      else {
         var count = 0
         var file
         var job = JSON.parse(msg)
         console.log('writing '+job.name+' (length '+job.contents.length+') to /dev/'+job.device)
         cancel = false
         fs.open('/dev/'+job.device,'w',function(err,fd) {
            if (err) {
               console.log('error: '+err)
               ws.send('error: '+err)
               }
            else {
               file = fd
               write_char()
               }
            })
         //
         // character writer
         //
         function write_char() {
            //
            // cancel
            //
            if (cancel) {
               console.log('cancel')
               ws.send('cancel')
               fs.close(file)
               }
            //
            // continue
            //
            else {
               fs.write(file,job.contents[count],function(err,written,string) {
                  if (err) {
                     console.log('error '+err+' count '+count)
                     ws.send('error '+err+' count '+count)
                     }
                  else {
                     ws.send((count+1)+'/'+job.contents.length)
                     count += 1
                     if (count < job.contents.length)
                        write_char()
                     else {
                        console.log('done')
                        ws.send('done')
                        fs.close(file,function(err) {
                           if (err) {
                              console.log('error: '+err)
                              ws.send('error: '+err)
                              }
                           })
                        }
                     }
                  })
               }
            }
         }
      })
   //
   // close
   //
   ws.on("close",function() {
      console.log("connection closed")
      })
   })